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Within the construction industry there is often confusionover gauges, gauge numbers and the actual thickness. Theindustry has been trying to move away from gauge numbers,

without complete success. The following information willshow why sheet steel products should be specified to thedecimal thickness.

Manufacturers Standard Gauge For

Steel SheetsThe most common gauge system used in Canada forstructural sheet steel products is the Manufacturers

Standard Gauge (MSG). The MSG for steel sheets wasdeveloped having a DEFINITE THICKNESS equivalent foreach gauge number. In the standard gauge system thedensity of steel is taken as 489.6 lbs/ft3, or 40.80 lbs/ft2/in.However, since sheet weights are calculated on the basis ofspecified width and length, with all shearing on the overside, and also since sheets are somewhat thicker at the centrethan they are at the edges, a further adjustment was madeto obtain a closer approximation for inter-changeabilitybetween weight and thickness. Over a long period of timethis value for sheets has been found to be close to 2.5 percent heavier than 40.80 lb/ft2/in. A figure of 41.820 lb/ft2/inis the one commonly used to express the relationship

between weight and thickness for steel sheet.

The Galvanized Sheet GaugeThe Galvanized Sheet Gauge is an older system usedprimarily by the trades consuming non-structural galvanizedsteel and is a measure of the zinc coated sheet thickness. It

was developed in the early days of galvanizing beforesophisticated wipers were available and, consequently, zincthicknesses were thicker than today. The GSG system wasused on some of the older gauge charts published years agothat unfortunately still seem to get used even today.

Thickness DefinitionsThere are a number of terms used for sheet steel productsthat need to be explained because they will affect thethickness of product that could be delivered to the job site.

Nominal Thickness: When sheet steel is produced by thesteel companies it is manufactured to a target or nominalthickness. As with all manufacturing processes, variations inthe final thickness of the sheet are unavoidable. However,the thickness is controlled very tightly to ensure that it doesnot fall below the minimum thickness (as described below).Base Steel Thickness: The thickness of the sheet steel material

without any coatings.

Coated Thickness:The thickness of the steel sheet includingany metallic coatings (i.e. zinc or 55% aluminum-zinc alloy)and paint coatings.Design Thickness: The design thickness is the thickness ofthe base steel only, and is used by the engineer to determinethe structural properties of the cold formed product. This isthe thickness that a manufacturer will list in their productcatalogues and load tables, where it could also be called thenominal base steel thickness.Minimum Thickness: The minimum thickness of structuralsheet steel building products delivered to the job site will be

the design thickness minus the maximum allowable under-tolerance specified by the CSA-S136-2007 Standard or thematerial specification, whichever is the more restrictive. Theminimum thickness allowed by the CSA-S136-2007 Standardis 95% of the design thickness.

Gauge NumberAnd Decimal ThicknessTable 1 shows the relationship between the MSG numbers,the nominal or design thickness, and the minimumthickness based on the CSA-S136-2007 Standard.

Minimum Thickness Allowancefor CoatingsSheet steel products are normally coated with a metalliccoating (i.e. zinc or 55% aluminum-zinc alloy), and also maybe painted. The minimum thicknesses of typical hot-dippedmetallic coatings are given in Table 2. The metallic coating

Sheet Steel Facts

C a n a d i a n S h e e t S t e e l B u i l d i n g I n s t i t u t e

April 2009

Sheet Steel Gauges and Thicknesses

8

10

12

13

14

15

16

18

2022

24

26

28

29

30

Minimum Base SteelThickness

(95% of Design Thickness)

GaugeNumber

Design Thickness(Nominal Base

Steel Thickness)

inches

0.1562

0.1278

0.0994

0.0852

0.0710

0.0639

0.0568

0.0454

0.03410.0284

0.0227

0.0170

0.0142

0.0128

0.0114

mm

3.967

3.245

2.524

2.164

1.802

1.624

1.443

1.153

0.8660.721

0.577

0.432

0.359

0.326

0.290

mm

4.176

3.416

2.657

2.278

1.897

1.709

1.519

1.214

0.9120.759

0.607

0.455

0.378

0.343

0.305

inches

0.1644

0.1345

0.1046

0.0897

0.0747

0.0673

0.0598

0.0478

0.03590.0299

0.0239

0.0179

0.0149

0.0135

0.0120

Table 1 - MSG Sheet Steel Gauge

Numbers and Thickness

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thickness must be added to the minimum base sheetthickness when determining the delivered sheet thickness.Metallic coatings are also subject to manufacturingtolerances the same as the base steel. Therefore, the actualthickness of the metallic coating will generally be greaterthan the minimums listed in Table 2. This factor needs tobe considered when attempting to verify the base steelthickness of a coated product.

Note: Minimum metallic coating thicknesses are total for both sides based

on Triple Spot Test per ASTM A653.

A significant amount of sheet steel is also prefinished witha paint system on top of the metallic coating. The thicknessof these paint/primer layers must also be included whenmeasuring the thickness of the sheet. The thicknesses oftypical paint coatings vary from 0.0003 to 0.001 in. (0.008to 0.025 mm) per side. Some thick film paint systems (e.g.Barrier Series) have thicknesses of 0.004 to 0.012 in. (0.100to 0.300 mm). Listed in Table 3 are the thicknesses ofcommon prefinished paint systems used in Canada.

Minimum Thickness for Common

Prefinished MaterialTable 4 shows the minimum thickness for a galvanized sheet

with a common paint system.

Additional Gauge Equivalents for

Steel StudsThe steel stud industry in Canada has in regular use additionalgauge number equivalents that are different than shown in Table 1.

Starting in June 2004, Canada will join the United States and adopta common set of standard base steel thicknesses for lightweight

steel framing components (e.g. studs and joists). These gauges areunique to this industry and are shown in Table 5. The CSA-S136-2007 maximum under-tolerance also applies to these gauges as wellas does the metallic coating allowances listed in Table 2.

ConclusionAn important thing to remember about gauge numbers is thatthey do not refer to only one thickness but instead represent a

range of thicknesses within the allowable tolerances, or todifferent thicknesses for different products. Gauge numbers arenot regulated and are generally used for convenience in salesliterature.Decimal thickness is required for structural designand material ordering. The steel industry encourages everyoneto use decimal thicknesses in specifying sheet steel productsand avoid the potential problems inherent with gauges.

For More InformationFor more information on sheet steel building products, orto order any CSSBI publications, contact the CSSBI at theaddress shown below or visit the web site at www.cssbi.ca

C a n a d i a n S h e e t S t e e l B u i l d i n g I n s t i t u t e

652 Bishop St. N., Unit 2A, Cambridge, Ontario N3H 4V6 Tel.: (519) 650-1285 Fax: (519) 650-8081

Coating

Designation

A01

A25

G01

G60

G90

AZ50

AZ55AZ60

Minimum

Thickness

(inches)

0.0004

0.0007

0.0004

0.0010

0.0015

0.0016

0.00180.0020

Coating

Designation

ZF001

ZF75

Z001

Z180

Z275

AZM150

AZM165AZM180

Minimum

Thickness

(mm)

0.010

0.018

0.010

0.025

0.038

0.041

0.0460.051

Table 2 - Minimum Metallic CoatingThicknesses

Paint

System

Perspectra Series, WeatherX

10000 Series

Elite and Metallic Series

Barrier Series 4 mil

Barrier Series 8 mil

Barrier Series 12 mil

Washcoat

inches

0.001

0.001

0.002

0.004

0.008

0.012

0.0003

mm

0.025

0.025

0.051

0.100

0.200

0.300

0.008

Nominal Thickness(1)

(1) The paint thicknesses listed are per coated side.

Table 3 - Thicknesses of Prefinished

Paint Systems

20

2224

26

28

29

30

Minimum Base Steel

Thickness

(95% of Design Thickness)

Gauge

Number

Minimum Coated

Steel Thickness(2)

inches

0.0341

0.02840.0227

0.0170

0.0142

0.0128

0.0114

mm

0.866

0.7210.577

0.432

0.359

0.326

0.290

mm

0.939

0.7940.650

0.505

0.432

0.399

0.363

inches

0.0369

0.03120.0255

0.0198

0.0170

0.0156

0.0142

Table 4 Minimum Thickness for

Prefinished(1) Sheet

(1) The sheet has a G90 (Z275) zinc coating (0.0015 in./0.040 mm), an8000+ Series paint coating on the finish side (0.001 in./0.025 mm)and a wash coat on the reverse side (0.0003 in./0.008 mm).

(2) Nominal paint thicknesses were used to calculate the overallminimum coated steel thicknesses.

Table 5 Standard Thicknesses forLightweight Steel Framing Components

(1) Minimum thickness represents 95% of the design thickness. Metric (mm)

minimum thicknesses were calculated by converting the Imperial (in.) values.

(2) A mil is 1/1000 of an inch (e.g. 30 mils is 0.030 inches).

Minimum Base

Steel Thickness(1)Designation

Thickness

Design

Thickness

Steel Framing

Gauge No. (for

reference only)(mils)(2)

18

30

33

4354

68

97

118

(mm)

0.455

0.752

0.836

1.0871.367

1.720

2.454

2.997

(in.)

0.0179

0.0296

0.0329

0.04280.0538

0.0677

0.0966

0.1180

(in.)

0.0188

0.0312

0.0346

0.04510.0566

0.0713

0.1017

0.1242

(mm)

0.478

0.792

0.879

1.1461.438

1.811

2.583

3.155

25

20 Drywall

20 Structural

1816

14

12

10